DE2145921A1 - DEVICE FOR THE PROCESSING OF MATERIALS USING A LASER RADIATION BUNDLE AND THE PROCESS FOR THEIR PRODUCTION - Google Patents

Description

lo. September 1971 8443-71 Dr.ν.B / Na

Günther NATH
8 Munich 23, Speyrer Str. 19

Device for material processing by means of a laser beam and methods of making them

The present invention relates to a device for material processing by means of a laser beam, with a laser and a flexible light guide. The invention also relates to a method for producing such a device.

Ss are devices for material processing, e.g. drilling, cutting and the like, by means of a laser beam known, in which the laser serving as the radiation source is fixed and the workpiece to be processed by a movable support with respect to the laser radiation beam can be displaced / grounded. Such facilities have become in the Precision mechanics and well proven in fixture construction, but they are only poorly suited for applications where the "laser beam tool" should be manipulated by hand, e.g. when engraving, in medicine and the like. For such tasks, on the other hand, it is known to arrange the laser firmly and a flexible one Provide light guide, one end of which receives the laser radiation beam, while the other end from which the laser radiation beam emerges, can be moved more or less freely by hand.

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The known devices of the last-mentioned type, however, still leave something to be desired in many respects. In particular, the transmission of the intense laser radiation, as it is needed for material processing, through a movable light guide causes considerable difficulties. Glass fiber light guides, which consist of a bundle of thin, optically isolated glass fibers, are damaged by high radiation outputs. The same applies to the self-focusing glass fibers and rods, in which the optical isolation is brought about by a parabolic change in the refractive index in the radial direction (magazine "Laser und angewandte Strahlentechnik ¹¹ No. 2/1971 pages 39-41), the usual diameter of such focusing glass fibers and There are also conical self-foe light guide rods known, the length of which can be, for example, 17 mm and the diameter of which can be 0.2 mm at one end and 1.0 mm at the other end Glass fibers and rods are made by replacing potassium ions with sodium ions in the initially homogeneous fibers and rods in a molten salt. Because of the high central refractive index of 1.6 and the sinusoidal light propagation with nodes of particularly high intensity, the same fibers are not resistant to high laser powers .

As a flexible light guide for intense laser radiation, as it is needed for material processing, so far it has practically only been possible to use mirrors that are articulated with one another connected arms are attached. However, such light guides are large, unwieldy and they have only limited flexibility, so that they cannot be used for many purposes.

Finally, it is also known to use a flexible tube with a highly polished inside as a flexible light guide Has gold layer. Even with such a light guide, the flexibility leaves a lot to be desired, and is metallic Mirror coating is relatively sensitive to radiation of high intensity

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did, as they did, for example, from pulsed lasers with high peak power is delivered.

Except for the sensitivity to high-intensity laser radiation the known light guides usually still have the disadvantage that they reduce the angular divergence of the transmitted radiation greatly enlarge and that the transmission leaves much to be desired especially when high transmission in a large spectral range is required. The above mentioned focusing Glass fibers and rods, for example, are not UV-permeable.

The present invention is accordingly the "

The object of the invention is to specify a device for material processing by means of a laser beam which has a very high radiation intensity lets through without the risk of damaging the device, which can be manipulated very easily by hand and which has a high efficiency, since the radiation losses are very small and the radiation because of the small increase The angle divergence of the radiation beam emitted by the laser can be focused on a very small area.

Gernäss the invention this object is achieved in a device of the type mentioned above characterized in that the light guide consists of a homogeneous quartz rod is, the side facing in a Λ the laser light entrance surface has mm a diameter of at least 3, corresponding to the diameter of the laser beam, then gradually to a flexible fiber-like part at least 400 mm long, the diameter of which is between 0.1 and 0.4 ram, tapers, then thickens again, ends in a light-emitting surface and is supported by spacers in a flexible tube that serves to protect against kinking.

The use of a material and optically extreme homogeneous quartz rod of the specified (known in principle)

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Form allows very high radiation outputs with small losses and a small increase in the angular divergence without the risk of damaging the quartz rod. Due to the relatively large radiation entry and exit areas (which are preferably anti-reflective) is the power density at the particularly endangered media boundaries relatively small.

In a first method for manufacturing a device according to the invention, a quartz rod is in a heatable and rotatable tube suspended at the free lower end with weighed down a weight, and the tube is then heated to such a temperature that a central part of the quartz rod is located pulls out to a thin fiber-like part with a diameter of about 0.1 to 0.4 mm.

In a second method for producing a device according to the invention, the particularly homogeneous light guide rods supplies, a quartz glass rod is inserted vertically into a tjuarzglas-dissolving Liquid, especially hydrofluoric acid, hung and rotated in this liquid, and it is between at least an interface of this liquid and the quartz glass rod brought about a relative movement in the axial direction of the quartz glass rod. .

Developments and refinements of the device according to the invention and the method for its production are characterized in the subclaims:

In the following the idea of the invention is based on the drawing explained in more detail, it show:

Fig. 1 shows an embodiment of a device for Material processing according to the invention;

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FIG. 2 shows a part of an embodiment which is somewhat modified from FIG. 1; FIG.

3 shows a schematic representation of an apparatus for producing a light guide rod for a device according to the invention, and

Fig. 4 is a schematic representation of another apparatus for producing a light guide rod for a device according to the invention.

In Fig. 1, as an embodiment of the invention, a working with a sharply focused laser radiation beam ^ Cutting tool shown, which is used in technology for material processing or in medicine for cutting and coagulating Tissue and the like. Can be used. The device contains a radiation source unit Io, which is not shown (on the ceiling of a work room or operating room) can be hung vertically and a high-power laser 12 as well an illumination laser 14 includes. With the high-power laser 12 For example, it can be a continuously operating YAGsNd laser act of a radiation beam 16 of about 1 ^ i wavelength supplies and e.g. can have a continuous output of 3o to 2oo watts. Since the radiation is in the invisible infrared range, is in the path of the radiation beam 16 by means of a part ι transparent mirror 18 and a deflecting mirror 2o a visible Radiation bundle 22 from the illumination laser 14 is faded in. The illuminating laser may, for example, be a He-Ne laser, or preferably a low power Kr laser, e.g. about 5 mW. Of course, you can use a conventional one for lighting in principle Use light source. For lighting purposes, achromatic light is generally preferable.

The combined radiation beam 18-22 emerges from the radiation source unit Io downwards into a tube 24, in

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which a further tube 26 is mounted telescopically displaceable. The bearing, which is not shown in detail, is designed in such a way that that the tube 26 can be pulled down a considerable distance and preferably automatically after being released returns to its upper position.

The tube 26 continues in a flexible tube 26 a, in which a light guide rod 28 through a number of spacers 3o is stored. At the lower end, the flexible tube 26a forms a type of nozzle 26b from which a protective gas emerges during operation, which is introduced through a connecting piece 32 on the tube 24 and prevents the light exit end of the Light guide rod 28 or a focusing optics arranged at this (Fig. 2) by vaporized or sprayed material becomes dirty.

The light guide rod 20 has a light entry surface 28 a _# provided with an anti-reflection layer 34, the diameter of which is preferably greater than 3 mm and can be, for example, 4.0 mm. A piece 28b of constant diameter adjoins the light entry surface 28a, followed by a piece 28c in which the light guide rod made of quartz glass gradually tapers to a thin fiber-like part 28d. The tapering part 28c is preferably at least 50 to 100 times as long as the diameter of the light entry surface, its length can be, for example, 20 to 40 cm with a diameter of the light entry surface of 4 mm.

The length of the fiber-like part 28d is preferably at least 400 mm, its diameter can be between 0.1 and 0.4 mm lie, it is preferably 0.3 mm.

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On the side of the fiber-like part 28 d facing away from the radiation source unit Io, the light guide rod in a piece 28 e again gradually thicker and ends in a light exit surface provided with an anti-reflection layer 36 28 f, which in the illustrated embodiment as a focusing Lens surface is formed.

The light guide rod 28 consists of homogeneous quartz glass of the highest optical quality. It is in its entire cross-section Materially and visually as homogeneous as Stand I technology and can be achieved with reasonable effort. An optical isolation of the light guide rod is caused by the blade-like spacers 3o, which consist, for example, of metal or magnesium fluoride crystals can and in the illustrated embodiment are designed so that the protective gas flow through the tube 26 can.

In order to be able to control the intensity of the radiation beam 16 or to be able to completely interrupt this radiation beam, the laser 12 is provided with an intensity control. The intensity control comprises a thin, ä with antireflection coatings provided plate 38 which is disposed in the optical resonator of the laser 12 between the resonator mirrors 4o. The plate is rotatably mounted about an axis running perpendicular to the axis of the radiation beam 16 and can be rotated by an adjusting device. The adjusting device can be controlled by a displaceable button 44 which is arranged at the handle end of the flexible tube 26 and is connected to an adjusting device (not shown), for example a sliding resistor, which in turn controls the device 42 via a connection indicated by dotted lines. By rotating the plate 38, the intensity of the radiation emerging from the high-power laser 12 can be controlled as desired and additional measures for switching off the laser radiation can be provided (if this is done by means of

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the plate 42 alone is not possible).

In FIG. 2, the end of the flexible light guide on the light exit side is a somewhat modified version compared to FIG Facility shown. The light guide rod 28 * has a flat light exit surface 28'f, which is also provided with an anti-reflection coating is provided. For focusing the essentially parallel one emerging from the light exit surface 28'f A focusing optics 46, for example consisting of a quartz lens, which is mounted in a wart tube 48, is used for the radiation beam, which is screwed onto the front end of the tube 26 * by means of a thread and can also be designed as a nozzle.

When the device is used for medical purposes, the focusing optics 48 are preferably easily removable or can be swiveled out of the beam path, so that the surgeon can quickly focus sharply between an egg-iem suitable for cutting Can change bundles and a bundle suitable for coagulation of larger cross-section. With a light guide rod 28 ' of the type shown in FIG. 2, the emerging radiation beam has a particularly small angular divergence. With the practical Embodiment with a total length of 120 cm, a diameter of the light entry and light exit area of in each case 4 mm and a diameter of the middle, fiber-like part of about 0.3 mm, the transmission was over 90% and the Divergence of 1 mrad of the incoming light beam provided by a He-Ne laser was determined by the light guide rod to only 1.2 degrees increased. (Full angle of the emerging cone of light). The low exit divergence of the laser light guide is crucial important for creating a sharp focal point by means of focusing optics. In contrast, has a fiber optic bundle light guide of the same length and a diameter of 5 mm a transmission of only about 48% and the divergence of the emerging light beam is 17 °. In addition, the fiber optic light guide does not hold any higher radiation output

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was standing. The light guide according to the invention transmits without damage a radiation power of 200 watts from a CW-YAG: Nd laser or pulse energies of several joules from a ruby laser. The length of the tapered part can be the same

the length of the part that is becoming thicker again. However, it is also possible to significantly increase the part that is becoming thicker again shorter, e.g. loo mm, than the tapered piece 28c (Fig. 1).

To produce a light guide rod made of quartz glass for a device according to the invention, one can use | make use of the apparatus shown schematically in FIG. 3. The apparatus contains a graphite tube 5o that of a quartz glass tube 52 is enclosed, into which a protective gas can be introduced through a connection piece 54. The graphite tube 5o can be heated by a high-frequency coil 56, which is connected to a non-illustrated coil 58 with a displaceable tap High frequency generator is connected.

A quartz glass rod 6o can be hung in the tubes 5o and 52.

When producing a light guide rod in Fig. 1 λ

or 2, the graphite tube is first brought to the temperature required for drawing the quartz glass thread and only then is a quartz rod, the end faces of which already have the final required optical processing, into the vertically standing graphite tube suspended and provided with a small weight 62 at the lower end. The temperature of the graphite tube should be so high that rapid heating of the quartz glass rod is guaranteed and recrystallization is avoided will. The temperature is preferably selected so high that a light guide rod of the type shown in FIG. 1 (diameter the light entry and light exit area of 4 mm, thickness of the fiber-shaped part 28d about 0.3 now) when using a device

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Io

Weight of approx. 150 g is pulled out to a length of approx. 600 to 150 mm within 2 minutes. The fibrous part does not get a constant diameter with this type of production, the diameter rather increases to a certain extent Point in the vicinity of the part 28 e which is becoming thicker again very slightly and then closes again. The conical shapes of the quartz rod can be defined in a defined manner by the vatiation of heating power, furnace geometry and weight to be influenced.

In the above-described thermal process for producing the light guide rod, optical Inhomogeneities arise that manifest themselves as fluctuations in the refractive index and increase the divergence of the transmitted light bundle and reduce the transmission. These inhomogeneities can practically not be eliminated by stress relief annealing, however, they are avoided in a chemical production process which is explained with reference to FIG.

The chemical manufacturing process is based on a quartz glass rod of the highest optical quality, the length of which is Corresponds to the length of the desired light guide rod and its thickness preferably equal to the thickness of the light entry surface as well as the end parts of the light guide rod which form the light exit surface is. Such quartz glass rods with a diameter of, for example, 5 to 7 mm are commercially available.

According to FIG. 4, it is about 100 cm long and about 5 mm thick quartz glass rod 7o of the highest optical quality in an approximately 15o cm high standing cylinder 72 made of acrylic glass. The standing cylinder 72 contains an approximately 20 percent by weight HF solution 74, below and above each of which there is one with it is immiscible liquid 76 or 78, which does not attack quartz glass. The specific densities of the liquids 76 and 78 are selected in such a way that the desired coating shown in FIG. 4 results.

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The standing cylinder 72 has an outlet 80 at the bottom with a valve 82 (e.g. a hose screw clamp), the enables the liquid to flow out of the standing cylinder 72 in a very slow, controlled manner.

The quartz glass rod 7o is rotated by a motor 84 at a speed of about 1 rev / sec.

The part of the quartz glass rod 7o rotating in it is uniformly etched away from, for example, 5 mm έ in diameter to 0.3 mm in diameter within a period of the order of magnitude of a few weeks through the dilute hydrofluoric acid solution. The outflow of the liquid and the slow sinking of the interfaces 86 and 88 between the hydrofluoric acid solution 74 and the liquids 76 and 78 result in the desired somewhat conical tapering or thickening parts of the light guide rod, the length of which can be changed by the outflow speed. The occurrence of concentration fluctuations in the hydrofluoric acid solution can be prevented by a small heating element (not shown) which generates a convection flow in the hydrofluoric acid solution.

The liquid 76, which for example consist of paraffin oil g

has the purpose of excessive evaporation of the hydrofluoric acid solution to prevent.

The surface of the in the manner described The light guide rod produced by etching is then polished, which can be done mechanically or chemically gradually reducing the concentration of the hydrofluoric acid solution or through the use of etchants that give a less coarse etch structure than hydrofluoric acid, e.g. ammonium hydrogen fluoride.

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Instead of the liquid flowing out of the standing cylinder 72 You can of course move the Ouarz rod 7o slowly in the axial direction or you can move the standing cylinder lower. If only a light guide rod thickened on one side is to be produced (i.e. a light guide rod with relatively small area light exit end) the lower liquid 78 not applicable.

Before the light guide rod is used in the desired shape using the described method? t and where applicable its peripheral surface has been polished, the end faces Ground, optically polished and provided with anti-reflective layers. The light guide rod is in the flexible tube 26 (Fig. 1) mounted.

The stiffness and flexibility of what serves as kink protection Hose or tube 26 is chosen so that the light guide rod Io can only be bent to such an extent that there is no risk of breakage consists. With a thread thickness of 0.3 mm, a minimum radius of curvature of approx. 3 cm is permitted without the risk of breakage.

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Claims (18)

2H5921 claims 1. Equipment for material processing by means of a laser beam, with a laser and a flexible light guide characterized in that the light guide (28, 28 ") consists of a homogeneous quartz rod which is attached to a light entry surface (28a) facing the laser (12) has a diameter of at least 3 mm, then gradually increases tapered to a flexible fiber-like part at least 400 mm long, the diameter of which is between 0.1 and 0.4 mm, then it becomes thicker, ends in a light exit surface (28f) and, through spacers (3o), in a kink protection serving flexible tube (26) is mounted. 2. Execution according to claim 1, characterized that the diameter of the light entry surface is 3 to Io mm. 3. Device according to claim 1 or 2, characterized in that the length of the tapered piece (28c) is at least 50 times, preferably at least 10 times the diameter of the light intact area (28a). 4. Device according to claim 1, 2 or 3, characterized geken n draws that the length of the in the direction of the light exit surface As the piece becomes thicker again, it is smaller than that of the tapering piece and preferably approx. loo ram amounts to. 30981? / 0A58 2U5921 5. Device according to one of the preceding claims, characterized in that the light exit surface (28f) is designed as a lens surface. 6. Device according to one of claims 1-4, characterized in that the light exit end of the light guide rod (28 ') has removable focusing optics (46) is attached. 7. Device according to einera of the preceding claims, characterized by a ei that the Lnde of the flexible tube (2G) located at the light exit side of the light guide (28) is formed as Schutzgasaustrithsaüse (26b). 8. Device according to claim 7, characterized in that the end facing the laser with a device (24, 32) is provided for feeding in a protective gas and that the flexible tube has a continuous Forms channel for the protective gas. 9. Device according to one of the preceding claims, characterized in that the laser (12) facing end of the flexible tube (26) mounted displaceably in the direction of the axis of the laser radiation beam (16) is. 10. Device according to claim 9, d a d u r ch y e k e η η ζ e i c h net that the end of the flexible tube facing the laser (26) is elastically biased towards the laser. 3098T? / (K58 2U5921 11. Device according to one of the preceding claims, characterized by a device (14, 18, 2o) for reflecting a bundle of visible light into den, put the laser beam (16). 12. fiinrichtung according to any one of the preceding claims, characterized in that in the optical Resonator (4o) dos lasers (12) has a rotatable plate (38) made of a material that is transparent to the laser radiation is and that the plate (38) by an adjusting device (42) to change the radiation power of the laser (12) " is rotatable. 13. Device according to claim 12, characterized in that the adjusting device (42) can be actuated by an actuating device (44) which is located at the light exit end of the flexible tube (26) containing the light guide rod (28). 14. Device according to one of the preceding claims, characterized in that the laser (12) is housed in a suspendable housing, on the underside of which the flexible tube (26) is attached. ^ 15. A method for producing a device according to claim l _f, characterized in that a vertical tube (5o) is heated to a temperature above the softening temperature of quartz glass, then a quartz glass rod weighted down with a weight (62) into the heated tube (6o), provided with optically p & osed end faces, so that the tube is cooled down when the quartz glass rod has stretched out to the desired length and is mounted in a flexible tube. 309817/0458 2H5921 16. A method for producing a device according to claim 1, characterized in that a quartz glass rod (7o) vertically in a quartz glass dissolving liquid, in particular hydrofluoric acid, is suspended and rotated in this liquid and that between at least one Interface (86, 88) of this liquid and the quartz glass rod a relative movement in the longitudinal direction of the quartz glass rod is brought about. 17. The method according to claim 16, characterized that the quartz glass rod is hung vertically in a vessel (76) that contains the quartz glass dissolving liquid (74) in such an amount that the quartz glass rod extends above the de.-i level of the liquid, and that above the level of this liquid there is a specifically lighter, hard-to-evaporate liquid that cannot be mixed with it Liquid (76) which does not attack quartz glass is arranged so that the quartz glass rod is rotated about its axis and that the level of the quartz glass-dissolving liquid (74) in the vessel (72) is slowly lowered. 18. The method according to claim 16 and 17, characterized in that below the quartz glass-less ends Liquid (74) is another liquid (78) which does not dissolve quartz glass and into which the quartz glass rod extends. 309812/0458 Blank page